Betaine is conventionally used for a humectant of cosmetics, a seasoning, a flavor-improving agent, and the like. Betaine has been industrially produced at a certain level, where betaine is recovered from beet molasses, a by-product generated with the production of beet sugar (sucrose), mainly by using a chemical method, a method using an ion exchange resin, and the like (e.g., PATENT LITERATURE 1).
In recent years, new effectiveness of betaine has been recognized in pharmacological activities, such as improvement of a liver disease and a heart disease and a muscle strengthening effect, and as dairy feed and aquaculture feed. Thus, the demand of betaine is expected to increase in the future.
However, betaine is so far produced on a scale relying on secondary use of the by-product in sucrose production and a method for intentionally producing betaine as a primary product is not available. Thus, actions for meeting such increasing demand are needed.
Moreover, particularly now, as a greater focus is placed on the global warming issue, controlling emission quantity of carbon dioxide gas, which is one of green house gases, and reducing a carbon dioxide concentration in the atmosphere by fixing carbon dioxide become major issues. Under such circumstances, fuel resources other than fossil fuels are needed, and there are growing expectations for developing biofuels using higher plants and microalgae as raw materials. It is known that productivity of organic materials per unit area of microalgae are 10 times or more higher than oil palm, which belongs to higher plants and whose productivity is considered relatively high. Thus, expectations are further growing for microalgae.
On the other hand, in constructing a large-scale process to recover carbon dioxide and produce organic materials using the microalgae, there are many cases where an exhaust gas from a thermal power plant and the like is expected to be a source of carbon dioxide. However, there is a problem in that the exhaust gas contains sulfurous acid gas that is harmful to plants and microalgae. For example, based on an environmental annual report created by a domestic coal-fired power station, it is estimated that an exhaust gas that is released to the atmosphere after desulfurization and denitration treatments still contains sulfurous acid gas of about 150 ppm on average and carbon dioxide of 3 to 15 vol. %.
After diluting the exhaust gas approximately 6 to 30 times with an air or the like to adjust the concentration of carbon dioxide (about 0.5 vol. %) so as to be suitable for blowing to a culture solution of microalgae, the exhaust gas still contains sulfurous acid gas having a relatively high concentration of 5 to 25 ppm. Sulfurous acid gas of this concentration is still harmful for the conventional microalgae to be used in the production of organic materials such as biofuels.
According to known knowledge, only red algae Galdieria disclosed in PATENT LITERATURE 2 is known to be resistant to sulfurous acid gas. On the other hand, a recent market request for algal biomass production becomes increasingly larger for various applications, such as bio-diesel fuel, hydrocarbon fuel, hydrogen gas/alcohol fuel, a raw material of chemicals, a raw material of healthy and functional food, and a raw material of medicines.
In other words, in the present situation, culturing the microalgae are required to provide, additionally to absorbing carbon dioxide, consistent business potential including the use and sale of biomass resulting from the absorption of carbon dioxide. In order to meet such various applications, it is desirable to find a number of sulfur dioxide gas-resistant algae other than the red algae Galdieria and respond to the various applications requested by the market based on the diversity of the algae.